The aim of the first national cross-sectional survey was to determine the prevalence of asthma-like respiratory symptoms and the associated risk factors among children aged 0-17 via interview with the parents by primary care physicians. They were selected through stratified two-stage cluster probability sampling in urban and rural parts of randomly selected 27 of 81 administrative districts in Turkey. Data was collected for 46,813 children (23,512 males and 23,301 females) of whom 66 percent resided in urban areas. The prevalence of physician-diagnosed asthma was 0.7 percent. The lifetime and current (last 12 months) prevalences were 14.7 percent and 2.8 percent for asthma, and 15.1 percent and 3.4 percent for wheezing respectively. The presence of personal atopy and history of family atopy were the most significant risk factors for current prevalences of wheezing, and asthma [adjusted Odds ratios (OR) and 95% confidence intervals (CI) were 6.2 (CI=4.0-9.5) and 1.8 (CI=1.3-2.4) for wheezing, and 8.5 (CI=5.6-12.9) and 1.9 (CI=1.4-2.5) for asthma, respectively]. Though there were no significant differences among those residing in urban versus rural areas regarding the current prevalences of asthma and wheezing, those living in coastal areas had considerably higher current prevalences than those inland (OR=2.6, CI=1.9-3.5 for wheezing, and OR=2.3, CI=1.7-3.1 for asthma). Residence in northern Turkey appeared to be a significant risk factor for wheezing (OR=1.9, CI=1.4-2.5), and children resident in southern Turkey exhibited the highest risk for occurrence of asthma (OR=1.5, CI=1.1-2.0) compared with eastern Turkey. In conclusion, the respiratory symptoms associated with asthma were an important cause of morbidity in childhood in Turkey. The discrepancy between prevalence of physician-diagnosed asthma and lifetime and/or current asthma prevalence figures may reflect the reluctancy of both physicians and parents to diagnose this condition. Besides strongest associations with personal atopy and atopic heredity, there w ere significant differences in prevalence rates between children residing in different regions, supporting the role of environmental factors.